Many vital organs, including the kidney, form as a result of a mesenchymal-epithelial interaction. A mediator of these interactions is hepatocyte growth factor, a. k. a. scatter factor, (HGF\SF). HGFISF is mesenchymally-derived growth factor and ligand for the epithelial c- rnet receptor. Though HGFISF is not the only inducer of renal development and tubulogenesis, it induces tubulogenesis both in vivo and in vitro ii Madin-Darby canine kidney (MDCK) cells, which are derived from canine renal tubular epithelium. Generation and maintenance of cell polarity is essential to epithelial cell function. To establish and maintain their polarity, epithelial, including MDCK, cells must send plasma membrane (PM) proteins to th( correct apical or basolateral PM. Preliminary results show that when HGF/SF induced tubulogenesis occurs MDCK cells lose their polarity as they branch out and then regain their polarity as the new tubules form. A major discovery in recent years is that almost all intracellular membrane traffic uses a common machinery for membrane fusion. Syntaxins are a gene family and component of the membrane fusion machinery that appear to specify correct delivery to the different PM surfaces. Syntaxins 2, 3, and 4 are abundant in epithelial organs, e.g. kidney. Syntaxins 2, 3, and 4 were found to be differentially expressed in MDCK cells, with syntaxins 3 and 4 having a completely non- overlapping distribution. Syntaxins are the first molecules that are part of the membrane fusion machinery, whose isoforms are differentially localized and whose overexpression has differential effects on polarized membrane traffic. Hence, they are the leading candidates for containing at least part of the information needed for the maintenance of cell polarity. The hypothesis is that transient loss of cell polarity i crucial for renal tubulogenesi: and syntaxins are involved in controlling cell poladty and therefore tubulogenesis. The expression and localization of syntaxins will be examined during HUF/SF induced tubulogenesis in MDCK cells, normal development of rodent kidneys, and abnormal development in disease states such a polycystic kidney disease and renal cell carcinoma. To directly test the hypothesis, the expression an function of different syntaxins will be perturbed by overexpression, inhibition of expression, and dominar negative mutants. If the expression of syntaxins is important for tubulogenesis, consideration can be given t finding ways to alter syntaxin expression in disease states, perhaps by gene therapy using viral vectors.